Enhanced 2-keto-L-gulonic acid production by a mixed culture of Ketogulonicigenium vulgare and Bacillus megaterium using three-stage temperature control strategy.

Abstract

As a key precursor of vitamin C, 2-keto-L-gulonic acid (2-KLG) was mainly produced from L-sorbose by mixed fermentation of Ketogulonicigenium vulgare and a helper strain (Bacillus spp.) with a low conversion rate for decades. The aim of this study was to enhance the 2-KLG production by co-culturing K. vulgare and Bacillus megaterium using three-stage temperature control (TSTC) strategy. By investigating the temperature effect on the 2-KLG fermentation, the optimum temperatures for the growths of K. vulgare and B. megaterium were 32°C and 29°C, respectively, while the optimum temperature for 2-KLG production was 35°C. We developed a TSTC process: the temperature was kept at 32°C during the first 16h of fermentation, then decreased to 29°C for the following 14h, and maintained at 35°C to the end of fermentation. By using this new process, the productivity and yield of 2-KLG from L-sorbose were obtained at 2.19 ± 0.19g/L/h and 92.91 ± 1.02g/L in 20-L fermentors for 5 batches, respectively, which were 22.35% and 6.02% higher than that of the control treatment (the single temperature of 29°C). The increased cell density of K. vulgare during the exponential phase and the enhanced SDH activity (increased by 25.18% at 36h, 17.14% at 44h) in the production stage might be the reasons for enhanced 2-KLG conversion rate and yield. Our results demonstrated the feasibility of the TSTC strategy for 2-KLG production.